1. Field of the Invention
This invention relates to a mixture heating unit for internal combustion engines, and more particularly to such evaporator in which a heating source is provided in the intake manifold and also a catalyst is utilized for markedly improving the heating effect.
2. Description of the Prior Art
In the conventional mixture heating units of the type contemplated, there is used a system in which a part of the intake manifold provided downstream of the carburetor is heated by exhaust gas or hot water (with the intake manifold having a hot water riser), but such indirect mixture evaporating method is incapable of providing sufficient heating at the time of engine start. Such method is also problematic from the viewpoint of purification of exhaust gas which has become an important problem confronting the industries concerned of late. That is, atomization and vaporization of fuel becomes imperfect due to insufficient heating from the very moment of engine start, and this causes a non-uniform mixture of fuel and air, resulting in improper fuel distribution into the combustion chamber in each cylinder, deficient output of the internal combustion engine, and non-smooth run of the engine. For eliminating these defects, it is required to supply an overrich mixture. Such non-uniformity or improper distribution of the mixture induces excess fuel supply and improper or imperfect combustion, resulting in increased discharge of unburned harmful gases such as CO and HC. For removing such problems, it is necessary to provide means that can ensure sufficient heating even at the time of starting and warm-up running of the internal combustion engine.